Glioblastoma (GBM) is among the deadliest cancers, characterized by poor prognosis and median survival of 12-15 months post-diagnosis. Despite aggressive therapeutic regimens, GBM treatment is still an unmet clinical need due to heterogeneity, recurrencies, and resistance. Metabolic reshaping is emerging as a critical mechanism supporting cell proliferation and sustaining chemoresistance. In this study, we explored metabolic changes induced by chemotherapy in temozolomide (TMZ)-sensitive and TMZ-resistant GBM cell lines. We found that purine levels were altered in sensitive versus resistant GBM cells, highlighting a critical role of guanosine and inosine metabolism. By using a mesenchymal-like GBM zebrafish model, we uncovered dysregulated pathways involved in purine metabolism, with a downregulation of catabolic processes. Our data indicate that combined treatment with TMZ plus guanosine and inosine increased cytotoxicity, enhancing chemotherapy effectiveness in TMZ-resistant cells. These effects correlated with alterations in mitochondrial dynamics and activity. Specifically, the combinatorial effectiveness of TMZ with guanosine and inosine was linked to Mitofusin-2 overexpression, enhancing mitochondrial fusion, typically associated with a better prognosis. Therefore, our findings suggest that purine metabolism is involved in the metabolic rewiring of TMZ-resistant cells, suggesting guanosine and inosine as potential adjuvant treatments to improve the cytotoxicity effects of chemotherapy in resistant GBM.